New knowledge on how to establish and manage planted birch
Birch trees may recover from light to moderate browsing damage. And heavy thinning resulted in the strongest individual tree diameter growth. These are some of the results in a new doctoral thesis from SLU by Andis Zvirgzdins.
The thesis focused on silver birch and particularly on spacing, browsing by cervids, thinning strategies, and modelling growth of genetically improved silver birch material.
Effects of browsing, spacing and thinning
”I was somewhat surprised by how tolerant silver birch proved to be to browsing. Even trees that lost their leader shoots multiple years in a row were able to maintain vitality and recover in height and diameter growth within a few years, showing strong compensatory growth capacity”, says Andis Zvirgzdins, former PhD student at the Southern Swedish Forest Research Centre at the Swedish University of Agricultural Sciences (SLU) and affiliated with Trees For Me.
In areas with a low to moderate browsing risk, the fast growth and compensatory ability of silver birch may reduce the need for intensive protection as the trees can escape the browsing window relatively quickly.
Overall, the browsing impact on birch in Sweden appears less severe than initially expected, according to the research results.
”While the short-term effects on tree quality were noticeable, the long-term effects might not be as severe as initially thought”, Andis Zvirgzdins.
However, protective browsing measures might be needed, especially in areas with a lot of moose and deer, since heavy browsing might cause long-term negative effects on growth and stem quality.
The results showed that wider spacing and fewer trees per hectare increased the diameter growth of the birch trees, while heavy thinning promoted individual tree diameter growth but reduced the total stand production. Establishing birch plantations with a higher initial density may help to dilute the browsing pressure. Such spacing strategies may help ensure a sufficient number of good-quality stems for future production; however, further research is needed to validate these assmuptions.
Inreased productivity and interest
According to the research results genetically improved birch seedling material and proper management can improve not only growth but also reduce the rotation length and boost the overall economy. Use of genetically improved planting material, clear management goals and consideration of site must guide each forest owner’s decision for the use of planted silver birch to be successful.
Advances in birch breeding and a need for more diversity in conifer-dominated forests, to increase biodiversity and reduce risks related to e.g. climate change, has contributed to an increased interest for planting birch among Swedish forest owners.
”Silver birch is one of the more promising species that could complement the forest landscape in Sweden”, Andis Zvirgzdins concludes, who will now continue his research career at Skogforsk.
More about the thesis
The research was conducted through short-term field trials, long-term experiments, and surveys in southern and central Sweden and Latvia, complemented by interviews with private forest owners in Sweden.
Contacts
Andis Zvirgzdins, former PhD student
Southern Swedish Forest Research Centre, SLU
andis.zvirgzdins@slu.se
Urban Nilsson, professor
Trees For Me and Southern Swedish Forest Research Centre, SLU
070-346 51 92, urban.nilsson@slu.se